1. Field of the Invention
The present invention relates to an illumination optical system and an image display apparatus including the same, and more particularly, to an illumination optical system including a light separation/integration device having a diffraction device, and an image display apparatus including the illumination optical system.
2. Description of the Related Art
FIG. 1 shows a conventional apparatus which uniformly illuminates a light valve, as disclosed in U.S. Pat. No. 5,625,738. As shown in FIG. 1, the conventional illumination apparatus includes a light source 4 having a focusing mirror 6, a collecting lens 8 which is disposed adjacent to the light source 4 and collects light from the light source 4, and a light tunnel 2 which receives the light collected by the collecting lens 8. The light tunnel 2 may be hollow with interior reflecting walls or have a space filled with a light transparent material. The light tunnel 2 has a length L and a rectangular cross section.
The light emitted from the light source 4 is incident on the light tunnel 2 at an angle “u” with a line 16, a longitudinal axis of the light tunnel 2, and while passing through the light tunnel 2, the intensity of the light is made uniform. The light is shaped through the light tunnel 2 and relayed to a light valve 12 by a relay unit 10.
To embody a color image, such a conventional illumination apparatus also includes a color filter (not shown), a color wheel (not shown), or an X-cube (not shown) as a color switching device on an optical path between the collecting lens 8 and the light tunnel 2 to separate the light according to predetermined wavelengths. However, where the light is separated using the color wheel or the color filter, only a single color light beam in white light passes through a predetermined region of the color wheel or the color filter. Accordingly, the light efficiency thereof is degraded. Where the X-cube is used, since the light incident from an existing light source diverges, a light reflectivity or transmissivity of a coating layer of the X-cube at a boundary decreases, decreasing the entire efficiency of the emitted light. This is because the reflectivity or transmissivity of the coating layer of the X-cube is dependent on a diverging angle of the light.
Additionally, an optical element, such as the light tunnel 2, that uniformizes the intensity of the light must be lengthened where a numerical aperture of the light incident from the light source 4 is small. Accordingly, it is difficult to manufacture a light weight and compact image display apparatus with the conventional optical element.